I'd very much appreciate some PA advice! I'm looking to buy a PA system for live performances with our acoustic duo. I'm the singer, with a pretty quiet voice and there's the guitarist who also sings backing. We have SM58's, and the guitarist has a monitor if we need it, so I'm looking for a portable PA with mixer which I can fit in my car. Budget is up to £450, and it will mainly be used for wedding receptions so I guess around 200 - 400 people max.

Along with some others here I do rate the Yamaha StagePAS you referenced. It's good value for money and pretty portable.

You might also want to checkout the various 'Dave' options from LD Systems. Again these are good value for money. If you went for a 'Dave' you'd probably need a small mixer too, but you needn't pay more than about £150-£175 for a decent one - secondhand would be cheaper as long as you shop with care. Consider the Soundcraft EPM/EPX series or the smaller Allen & Heath ZEDs.

The new hyper-portable system from HK Audio seems attractive, BUT it's almost certainly not powerful enough for what you need - as well as being slightly above budget.(If you subscribe to SoS, Paul White did a recent review.)

You might want to look at the bigger version of the Yamaha unit you linked to as it looks like you'll be doing some fairly large gigs. If you have a quiet voice I would also recommend you take a look at the Audix range of vocal mics - the OM5 sounds good through the Stagepas system in my experience or the OM7 will be more useful if feedback is a problem.